feat: add 3-tier memory layer

agent_service/memory/conversation_store.py

@@ -0,0 +1,47 @@
+from __future__ import annotations
+import logging
+
+logger = logging.getLogger(__name__)
+HARD_CAP = 200
+
+
+class ConversationStore:
+    def __init__(self, pool):
+        self._pool = pool
+
+    async def append(self, user_id, role, content, directive_id=None, is_summary=False):
+        async with self._pool.acquire(timeout=10) as conn:
+            await conn.execute(
+                """INSERT INTO ab_conversation_memory
+                   (user_id, role, content, directive_id, is_summary)
+                   VALUES ($1, $2, $3, $4, $5)""",
+                user_id, role, content, directive_id, is_summary)
+
+    async def get(self, user_id, limit=50):
+        async with self._pool.acquire(timeout=10) as conn:
+            rows = await conn.fetch(
+                """SELECT id, role, content, directive_id, is_summary, created_at
+                   FROM ab_conversation_memory
+                   WHERE user_id = $1
+                   ORDER BY created_at DESC LIMIT $2""",
+                user_id, limit)
+        return [dict(r) for r in reversed(rows)]
+
+    async def count(self, user_id):
+        async with self._pool.acquire(timeout=10) as conn:
+            row = await conn.fetchrow(
+                'SELECT COUNT(*) as n FROM ab_conversation_memory WHERE user_id = $1 AND is_summary = false',
+                user_id)
+            return row['n']
+
+    async def prune_old(self, user_id, keep=50):
+        async with self._pool.acquire(timeout=10) as conn:
+            await conn.execute(
+                """DELETE FROM ab_conversation_memory
+                   WHERE user_id = $1 AND is_summary = false
+                   AND id NOT IN (
+                       SELECT id FROM ab_conversation_memory
+                       WHERE user_id = $1 AND is_summary = false
+                       ORDER BY created_at DESC LIMIT $2
+                   )""",
+                user_id, keep)